The present invention relates to an information-reading head apparatus for reading information from an information-bearing means such as a magnetic disk, a magneto-optical disk, a member to be subjected to a surface roughness test, etc.
In the case of a magnetic disk drive, for instance, as shown in FIG. 9, it comprises a magnetic disk 30 rotating at a constant speed, and a magnetic head 31 movable in a radial or tangential direction of the magnetic disk 30 for conducting the reading and writing of information of the magnetic disk 30. It is well known that to achieve a high record density and a high data transfer speed, most types of magnetic disk drive comprise floating (flying)-type magnetic heads which can stably maintain floating (flying) distance between their magnetic gaps and magnetic disks. In such a floating-type magnetic head, upward dyanamic pressure caused by the viscosity of the an air fast moving together with the magnetic disk 30 relative to the magnetic head 31 is utilized to maintain a flying distance (a small gap) between the magnetic head 31 functioning as a transducer and the magnetic disk 30.
A magnetic head having a portion which generates the above upward dynamic pressure (usually called "floating surface") is called "monolithic head." A typical monolithic head is a Winchester-type head. There is another type of a floating magnetic head called "composite-type head," which comprises a slider having a floating surface and a magnetic core bonded to a slit formed in the slider with bonding glass. Further, there is a thin-film magnetic head which has a magnetic thin film formed on a ceramic substrate for constituting a magnetic transducer.
In any magnetic head, its substrade (slider) is made of a mpm-magnetic material such a Al.sub.2 O.sub.3 -TiC, ZrO.sub.2, CaTiO.sub.3, etc and the magnetic core functioning as a transducer is made of a magnetic material such as Mn-Zn ferrite, Ni-Zn ferrite, etc.
Each of these magnetic heads is supported by a suspension and pressed onto a disk surface by a spring force of the suspension when the magnetic disk is not rotating. When the magnetic disk starts rotating, upward dynamic pressure is generated by the air flow, so that the magnetic head floats at a height at which the upward dynamic pressure is balanced with the spring force. And when the magnetic disk stops rotating, the magnetic head again comes into contact with the magnetic disk. This system is called "contact start stop (CSS) system."
In addition to the above magnetic disk drives using a CSS system, there is a disk pack-type magnetic disk drive in which a magnetic disk is replaceable. In this magnetic disk drive, a magnetic head called "ramp head" is used.
The support of the magnetic head by a suspension is usually achieved as shown in FIGS. 9, 10 (a). The suspension 3 comprises a head arm 34, a load arm 33 fixed to a tip end portion of the head arm 34, and a gimbal 32 fixed to a tip end portion of the load arm 33. The load arm 33 is generally in a flat plate shape extending in a radial direction of the magnetic disk 30. The gimbals 32 is constituted by a lip portion fixed to a tip end portion of the load arm 33, a base portion to which a magnetic head 31 is fixed, and a pair of link portions integrally extending between the lip portion and the base portion such that it can absorb an external force applied to the magnetic head 31 when coming into contact with the magnetic disk 30.
The head arm 34 is supported by a head arm-moving apparatus (not shown) which enables the magnetic head 31 supported by the suspension 3 to move in a radial or tangential direction with respect to the magnetic disk 30. This head arm-moving apparatus is usually called "positioner" or "actuator." This head arm-moving apparatus comprises a carriage supporting the head arm 34 and a motor for actuating the carriage. The carriage has a linear-type or rotary-type mechanism. A control system for positioning the magnetic head 31 includes an open loop system in which a stepping motor is used, an a closed loop system in which a voice coil motor (VCM) is used. In the case of the closed loop system, there are several systems depending on the method of treating a positioning signal. A system most widely used today is a servo-control system utilizing a servo disk.
Incidentally, there has recently been developed a suspension for a load arm called "inline-type load arm." The inline-type load arm extends in a tangential direction of the magnetic disk 30. With respect to other portions, they are substantially the same as described above.
With respect to the magnetic head 31, it is floated as follows: First, when the magnetic disk 30 is stationary, the magnetic head 31 is slightly pressed onto the magnetic disk 30 under a load of about 10 gf exerted by a spring force of the suspension itself. When the magnetic disk 30 starts rotating, the magnetic head 31 starts floating. A rotation speed of the magnetic disk 30 necessary for floating the magnetic head 31 is, for instance, 4 m/sec. The floating height is usually 0.15-0.5 .mu.m.
Since the magnetic head 31 is usually resting on a disk surface when the disk 30 is not rotating, it is likely that the magnetic head 31 is dragged rearward relative to the suspension 3 by a large friction between the magnetic head 31 and the disk surface. Such a large friction is caused by sticking of the magnetic head 31 to the disk surface due to moisture, etc. When the magnetic head 31 is dragged rearward, the gimbal 32 is deformed as shown in FIG. 10 (b). By this deformation, a front portion of the magnetic head 31 is directed downward. Namely, the magnetic head 31 pitches forward. This "pitch-forward action" of the magnetic head 31 is likely to cause damage to the disk surface.
Also, during the floating period, it is likely that the floating magnetic head 31 comes into contact with the rotating magnetic disk 30 due to the vibration of the magnetic head 31 caused by an external force, or due to the surface roughness of the magnetic disk 30, etc. Also, in the case of landing of the magnetic disk 30, the magnetic head 31 is dragged on the disk surface, or it bounces on the magnetic disk 30 before complete stop.
At the time of landing, the magnetic head 31 is also likely to pitch forward due to a large friction as in the case of taking off.
In such a CSS-type magnetic disk drive, when the magnetic head comes into contact with the magnetic disk during the operation for reason as mentioned above, the magnetic head tends to pitch forward. One reason therefor is that the magnetic head has a center of gravity substantially at a center of support thereof. Another reason is that the conventional gimbals support the magnetic head such that the magnetic head is not resistant to pitching. This pitch-forward action of the magnetic head gives severe damage to the surface of the magnetic disk, extremely reducing the service life of the magnetic disk. In general, the magnetic disk is required to endure more than 10,000 CSS cycles. However, if there is severe damage caused by the above action, the CSS cycles are as small as 5.000 or so.
Incidentally, to avoid such damage, there has been proposed a so-called load-unload system in which a magnetic head is always kept above a magnetic disk even at the time of start and stop. However, a suspension constituted by a horizontal flat plate is easily twisted, and a gimbal is little resistant to pitching forward and rearward. As a result, it is impossible to prevent the magnetic head from pitching forward and rearward, namely from coming into contact with the magnetic disk in its front or rear portion during the operation.
The problems with the conventional magnetic disk drives are explained above, but the same is true with respect to magneto-optical disk drives, etc.